1. Field of the Invention
This invention relates to steam generating systems in general and more specifically, to a system for automatically injecting a cool water mist into a steam bound boiler feed pump.
2. Background of the Invention
In a typical steam generator, a hot water boiler is fed by a centrifugal boiler feed pump. For a variety of reasons it is not unusual for such pumps to become "steam bound" and when this occurs, the efficienty of the boiler pump drops considerably. To overcome this condition, the steam plant operator often has to cool down the steam bound pump by applying cold water to its exterior housing. Several other approaches are discussed in the prior art. For example, Vogler U.S. Pat. No. 3,126,875 discloses injecting cold water into the intake side of a water pump in order to eliminate vapor lock therein. The cold water is injected into the pump in response to a pressure differential measuring device which monitors the pressure in a hot water tank. Similarly, British Pat. No. 343,385 discloses injecting a second liquid into a centrifugal pump and calls for the liquid to be under pressure and to enter the pump through a plurality of nozzles located in the housing. Other prior art references of relevance include: Hariveau U.S. Pat. No. 1,581,204; Hutton U.S. Pat. No. 3,286,639; Jackson U.S. Pat. No. 3,504,986; German Pat. Nos. 304,763; 475,711; and 556,579; and British Pat. No. 308,442.
Unfortunately, the techniques disclosed by the prior art are often complicated, both in structure and function. Since the problem of steam bound boiler feed pumps is common, a direct and straight-forward solution to this problem was sought. Additionally, the problem of steam bound pumps is frequently associated with low water boiler failures. For example, a total of 44 accidents occurred due to low water failures in power boilers during the period of January 1, 1973 through December 31, 1973 as reported by the National Board of Boiler and Pressure Vessel Inspectors. Those accidents resulted in four known injuries. Similarly, low water failures resulted in 78 accidents in heating boilers during the same period. These statistics only reflect reported insurance accidents and do not take into account factors such as lost production time and boiler damage repair cost. For example, if the boiler tubes burn out they must be replaced and the plant must be shut down during the replacement period. While not all low water failures are attributable to malfunctioning feed pumps, nevertheless, malfunctioning pumps are believed to be a significant factor in such difficulties. Therefore a means was sought which would prevent low water boiler failures due to steam bound pumps. This, of course, would increase the safety of steam generators and generally improve reliability. The factor of reliability is very important, since it is often necessary to have a complete steam generator system in standby condition ready for operation if the use of steam is critical. For example, a naval man of war in the attack condition; a petroleum oil cracking tower or a hospital must be able to maintain steam power under all conditions. By automatically eliminating the steam bound pump condition, it may be possible to eliminate the necessity of a secondary system in such steam generating operations. Therefore, from the safety and reliability point of view, the ability to automatically clear a steam bound boiler pump is a very important capability. It is believed that the present invention has applicability to a wide range of prior art steam generators, including stationary, marine, locomotive and portable boilers. Also, while a centrifugal pump is used as an illustrative example, it is to be understood that this system may be applied to many other pumps known in the prior art. It was in the context of the foregoing prior art that a simple, safe, efficient and reliable means was sought to solve the problem of steam bound boiler feed pumps.